Biology Honors Thesis
Molecular Characterization of pmh1 : A Chlamydomonas reinhardtii Mating Mutant That Fails to Agglutinate During Sexual Reproduction
Toh Hean Ch'ng
Class of 1999
Mentor : Dr. A. Malcolm Campbell
Co-Mentor : Dr. John H. Williamson
Department of Biology
Davidson College
Davidson, NC 28036
Abstract
Chlamydomonas reinhardtiiis a biflagellated green alga that carries out sexual reproduction under stressful conditions. Sexual reproduction of wildtype C. reinhardtiiis mediated by flagellar agglutinins that are O-linked glycoproteins. pmh1 is a mating-type minus mutant strain which fails to agglutinate and thus is unable to form the diploid zygote. Northern blot analysis of pmh1revealed the absence of a 4.4 kb mRNA message which is normally expressed in wildtype gametic and vegetative cells. The putative pmh1gene has been cloned and sequenced. With the completion of one of the two genomic constructs, complementation experiments of the pmh1 gene to rescue the phenotype are being carried out. The putative wildtype pmh1gene shows a strong sequence homology to a plasma membrane H+-ATPase. However, the low relational similarity of the pmh1gene with other organisms suggests that pmh1gene may code for a novel H+-ATPase that might not be localized in the plasma membrane. It is hypothesized that the absence of H+-ATPase will alter the intracellular pH which leads to improper glycosylation of glycoproteins. As a result of improper glycosylation, non-functional agglutinins are produced and this leads to the failure of flagellar agglutination in pmh1mutant cells.